Efficacy of 2- and 4-week rifampicin treatment on the Wolbachia of Onchocerca volvulus.

The microfilaricidal and temporarily sterilizing drug ivermectin is used for mass treatment of filarial infections. Filariae containing Wolbachia endobacteria can also be treated by the antibiotic doxycycline. The loss of Wolbachia results in sterilization of Onchocerca volvulus and macrofilaricidal effects. Besides doxycycline, other antibiotics may be effective in depleting Wolbachia. A preliminary study on the effects of rifampicin on the endobacteria, embryogenesis and microfilariae production of O. volvulus was carried out in the year 2000 in Ghana. Twenty-six onchocerciasis patients were treated for 2 or 4 weeks with 10 mg/kg/day rifampicin. From 17 treated and nine untreated patients, all palpable nodules were extirpated 1 or 18 months after the start of the study and examined for Wolbachia and embryogenesis using immunohistology. One and 18 months after rifampicin treatment, the proportion of Wolbachia-positive worms was significantly reduced compared to the untreated group. In patients treated 4 weeks with rifampicin, only 21% and 18% of living female filariae contained Wolbachia after 1 and 18 months, respectively, compared to 92% in the untreated patients. The reduction of Wolbachia after 2 weeks rifampicin was less but also significant. Embryogenesis and microfilariae production were reduced after 4 weeks rifampicin treatment, rendering rifampicin an antibiotic with anti-wolbachial efficacy in human onchocerciasis. This treatment is less efficient than treatment with 6 weeks doxycycline, but might be an alternative for cases that cannot be treated with doxycycline, e.g. children, or might be further developed for combination therapy.